Windows of the tiltable type, in particular of the kind adapted to be installed in sloping roofs, must satisfy heavy demands with respect to weathertightness and in general they therefore comprise an inner rabbet or abutment fillet aiming particularly at eliminating draft, and an external metallic or plastic covering primarily intended to prevent rainwater from penetrating between the stationary frame and the sash of the window. The rabbet fillet as well as the outer covering are necessarily divided at the pivot axis, i.e. in the areas of the hinge devices, the portions of the fillet and covering above the axis being secured to the frame, while the portions below the axis are mounted on the sash so as to follow the movements thereof. A condition of an optimum tightness is that the rabbet fillet forms a tight closure below the hinges, thereby restricting the permissible depth of the hinges, i.e. their dimension perpendicular to the plane of the window, but it is even more important that the hinges guide the sash so as to allow a sufficient overlapping, in the closed position of the window, between the movable and non-movable parts of the outer covering without causing these parts to prevent a tilting of the window sash through approximately 180.degree., or without causing the parts to be damaged by such a movement of the sash.
The sash should moreover be balanced in such a manner that, at least within certain open positions, it remains immovable in any angular position in relation to the stationary frame, and it should further be easily mounted in and dismounted from the frame, for instance with respect to changing its pane.
These requirements are considered to be fulfilled by a hinged device of the kind illustrated in FIGS. 6 and 7 of British patent specification No. 1,028,251 which discloses a tilting window hinge device comprising frame and sash portions having a curved guide and a correspondingly shaped sliding rail, respectively, which together define a tilting axis located at a slight distance outside the outer surface of the window. The sliding rail member of the sash portion is connected to the base plate of the same portion through a pivot pin allowing a further tilting of the sash after the termination of the displacement of the sliding rail member along the curved guide of the hinge portion of the frame.
In a hinge structure of this design it is difficult to control the frictional properties of the sliding rail and guide members and, consequently, to control the balancing conditions of the window sash without preventing a conveniently easy opening and closing movement of the sash. A further fact is that the prior art hinge in practice must include a large number of components which may well be produced relatively cheaply, but still they require rather expensive stamping tools and many assembling operations.